The present invention relates to a system for performing control of an engine and diagnosing the control of an engine.
It has been known in the art to increase the amount of HC (hydrocarbon that is unburned fuel and reformed HC due to combustion) in exhaust gas by performing fuel injection divided into a plurality of parts through a fuel injector that sprays fuel directly into a combustion chamber. For example, fuel injection control is performed by spraying fuel through main fuel injection only at a point of time near a top dead center of a compression stroke while an engine operates in ordinary engine operating conditions. In order to increase the HC concentration of exhaust gas, the fuel injection control is performed by spraying fuel through post-fuel injection subsequently to the main fuel injection according to engine operating conditions when necessary. In the case where NOx trapping substance operative to absorb NOx in exhaust gas is provided in an exhaust gas passage, the amount of the HC concentration of exhaust gas is increased for the purpose of causing the NOx trapping substance to release NOx or supplying HC as a deoxidizing substance to a catalyst for purifying exhaust gas by deoxidizing NOx in the exhaust gas.
Japanese Unexamined Patent Publication No. 8-200045 discloses a system having a NOx trapping substance in an exhaust passage which performs fuel injection at a point of time near a top dad center in a compression stroke while an engine operates in ordinary engine operating conditions. The system performs post-fuel injection in either an expansion stroke or an exhaust stroke, additionally to the main fuel injection that is implemented at a point of time near the dead top center of the compression stroke, so as to decline an exhaust gas air-to-fuel ratio when releasing NOx from the NOx trapping substance. The term xe2x80x9cexhaust gas air-to-fuel ratioxe2x80x9d as used herein shall mean and refer to a ratio of the entire amount of air relative to the entire amount of fuel in exhaust gas. NOx released from the NOx trapping substance reacts on HC or CO on a noble metal catalyst such as platinum and the like and then is deoxidized. The system that Japanese Unexamined Patent Publication No. 8-200045 discloses is configured and adapted to close an exhaust gas recirculation passage so as to prevent recirculation of a large amount of unburned fuel from being admitted into an intake stream when implementing fuel injection for refreshing the NOx trapping substance while the engine operates in a region of lower and moderate engine loads where a large amount of exhaust gas is expected to be recirculated.
In the case of increasing the HC concentration of exhaust gas by means of altering the mode of fuel injection, it is definitely required that the mode of fuel injection is altered as previously scheduled. Therefore, it is preferred to ascertain whether a fuel injection mode is normally altered as scheduled. As a means for ascertainment of a normal alteration in fuel injection mode, an HC sensor may be disposed in the exhaust gas passage to detect the HC concentration of exhaust gas. A change in output from the HC sensor is checked at an occurrence of an alteration in fuel injection mode in order to make a decision as to whether or not the fuel injection mode alteration control is normal or should be corrected. However, because exhaust gas contains different kinds of HC, detection of HC concentrations of the exhaust gas by the HC sensor is hardly accurate.
In place of detecting the HC concentration of exhaust gas, it may be carried out to detect the concentration of oxygen (O2) or NOx of exhaust gas. That is, since a change in HC concentration of exhaust gas is revealed as a change in exhaust gas air-to-fuel ratio or oxygen concentration of exhaust gas, a change in HC concentration of exhaust gas is monitored indirectly by monitoring the oxygen concentration of exhaust gas. In the case where a NOx deoxidizing catalyst is provided in the exhaust gas passage, since an increase in HC concentration of exhaust gas quickens deoxidization of NOx, the NOx concentration of exhaust gas declines as the HC concentration of exhaust gas increases. On the grounds, a change in HC concentration of exhaust gas is monitored indirectly by monitoring the NOx concentration of exhaust gas.
However, though the oxygen sensor is suitable for detection as to whether an exhaust gas air-to-fuel ratio is near a specific ratio, nevertheless, the oxygen sensor is hard to detect a wide range of oxygen concentrations of exhaust gas even if it is of a linear type. There are less types of NOx sensors that are simple in construction and capable of accurately detecting NOx concentrations of exhaust gas. Further, because HC is low in reactivity on O2 or NOx while the exhaust gas is at low temperatures, so that it is hard to detect accurate HC concentrations of exhaust gases. In addition, processing an output from the sensor is apt to make control complicated.
It is an object of the present invention to provide an engine control system which is capable of diagnosing whether not only fuel injection mode alteration control but also a change in composition of exhaust gas are achieved as expected without using a sensor which detects a component concentration of exhaust gas.
It is another object of the present invention to provide an engine control system which is capable of correcting fuel injection mode alteration control without using a sensor which detects a component concentration of exhaust gas.
The foregoing objects of the present invention are accomplished by diagnosing normality or abnormality of the fuel injection mode alteration control or correcting the fuel injection mode alteration control on the basis of engine output which varies according to a HC content of recirculated exhaust gas.
According to an aspect of the present invention, the diagnostic system for diagnosing normality or abnormality of control of an engine which is equipped with a fuel injector for supplying fuel into the combustion chamber, exhaust gas control means for controlling a change in composition of exhaust gas from the engine so as to cause a change in HC concentration of the exhaust gas according to engine operating conditions and an exhaust gas recirculation system for recirculating partly exhaust gas into an intake system of the engine comprises output detecting means for detecting engine output of the engine and diagnostic means for making a diagnosis of normality or abnormality of the control of the change in composition of the exhaust gas when the engine output does not causes a predetermined change meeting to the change in HC concentration of the recirculated exhaust gas after the change in composition of the exhaust gas.
When the exhaust gas control means controls a change in composition of exhaust gas so as to causes a change in HC concentration, since exhaust gas is partly recirculated into an intake system of the engine, the HC content of burned gas in the combustion chamber of an engine varies with a time lag behind the change in composition of the exhaust gas as long as the control of a change in composition of exhaust gas is performed as expected. The change in HC content of exhaust gas appears as a change in engine output. When the engine output does not change correspondingly to a change in composition of exhaust gas, namely, a change in HC concentration of recirculated exhaust gas as expected, this indicates that the change in composition of exhaust gas fails to meet the expectation, then the control of a change in composition of exhaust gas is regarded as abnormal. The change in composition of exhaust gas such as to cause a change in HC concentration such as, for example, a change in fuel combustion in the combustion chamber, is achieved by an alteration of fuel injection mode such as a change in the amount of fuel injection, a change in the number of times of fuel injection or a change in fuel injection timing, or a change in ignition timing if the engine is of a spark-ignition type. Therefore, when the control is judged to be abnormal, it can be said that the fuel injector or its control system, or the ignition device or its control system fail to operate normally.
Employed as the output detecting means is one operative to detect a physical value (magnitude of shaft torque, a fluctuation in shaft torque, a change rate of shaft torque, an angular speed of an crankshaft, etc.) relating to shaft torque of the engine which periodically changes. The diagnosis of normality or abnormality of the control on the basis of a physical value detected by the output detecting means, more specifically, on the result of comparison of the physical value with a judging threshold value.
In the case where the fuel injector is disposed so as to spray fuel directly into the combustion chamber of the engine, the exhaust gas control means controls a number of times and timings of fuel injection in a period from the beginning of an intake stroke and an end of an exhaust stroke according to engine operating conditions.
A sensor operative to detect oxygen concentration or NOx concentration of exhaust gas may be provided downstream from an inlet of an exhaust gas recirculation passage. When the oxygen concentration of exhaust gas is lower than a judging threshold value or when the NOx concentration of exhaust gas is higher than a judging threshold value, the diagnosis of normality or abnormality of the control by the diagnostic means can be restrained. That is, the fact that the oxygen concentration of exhaust gas is lower than the judging threshold value or the fact that the NOx concentration of exhaust gas is higher than the judging threshold value indicates that the exhaust gas which is not recirculated and is directed to the sensor contains a large amount of HC, in other words, that the amount of recirculated exhaust gas is small. In this event, because the recirculation of exhaust gas has a less influence on engine output, due to which a diagnosis error is apt to occur, the control by the diagnostic means can be restrained.
In place of restraining the diagnosis of normality or abnormality of the control, it may be done in order to make a diagnosis either to increase the amount of exhaust gas recirculation, to change the judging threshold value, or to change a combustion state so as to increase the amount of HC in exhaust gas by, for example, increasing the amount of fuel injection.
According to another aspect of the present invention, the diagnostic system diagnoses normality or abnormality of control of an engine which is equipped with a fuel injector for supplying fuel into the combustion chamber, exhaust gas control means for controlling a change in composition of exhaust gas from the engine so as to cause a change in HC concentration of the exhaust gas according to engine operating conditions and an exhaust gas recirculation system for recirculating partly exhaust gas into an intake system of the engine. The diagnostic system comprises output detecting means for detecting engine output of the engine, fuel injection control means for detecting a change in the engine output following a change in HC concentration of the recirculated exhaust gas and feedback controlling an amount of fuel injection, that is sprayed by the fuel injector, on the basis of the engine output so as to provide a predetermined engine output, and diagnostic means for making a diagnosis of abnormality of the control of the change in composition of the exhaust gas when a feedback control value for the amount of fuel injection exceeds a predetermined extent.
Since the feedback control value corresponds to a deviation of an actual change in HC concentration of exhaust gas due to the change in composition of exhaust gas from an expected change in HC concentration of exhaust gas, if the feedback control value exceeds the predetermined extent, namely, the variation is too large, this indicates that the composition of the exhaust gas is not changed as intended, then, the control is judged to be abnormal.
According to another aspect of the present invention, the engine control system for controlling of an engine which is equipped with a fuel injector for supplying fuel into the combustion chamber, exhaust gas control means for controlling of a change in composition of exhaust gas from the engine so as to cause a change in HC concentration of the exhaust gas according to engine operating conditions and an exhaust gas recirculation system for recirculating partly exhaust gas into an intake system of the engine comprises output detecting means for detecting engine output of the engine and correction means for detecting a change in the engine output following the change in HC concentration of the recirculated exhaust gas and correcting the control of the change in composition of the exhaust gas on the basis of the change in the engine output.
When a change in composition of exhaust gas causes a change in HC concentration of the exhaust gas, the amount of HC appears as a change in engine output. Therefore, if the engine output does not correspond to a change in composition of the exhaust gas, the control of HC concentration of the exhaust gas is corrected so as to provide engine output corresponding to a change in composition of the exhaust gas.
As stated above, because, when engine output does not change correspondingly to a change in HC concentration of exhaust gas from the combustion chamber that is caused following a change in composition of the exhaust gas, it is decided that the change in composition of the exhaust gas is abnormal, the diagnostic system is simply configured without using a sensor which detects the component concentration of exhaust gas. Moreover, the diagnostic system is capable of diagnosing normality or abnormality of the engine control irrespective of exhaust gas temperature.
Further, because exhaust gas composition control is corrected on the basis of a change in engine output following a change in HC concentration of recirculated exhaust gas when the composition of exhaust gas from the combustion chamber so as to cause a change in HC concentration of the exhaust gas, the engine control system is simply configured without using a sensor which detects the component concentration of exhaust gas. Moreover, the engine control system is capable of correcting the exhaust gas composition control irrespective of exhaust gas temperature.